Reversing chiral selectivity in optical trapping via Babinet complementary metasurfaces

We systematically investigate the chiral trapping mechanism of Babinet complementary plasmonic metasurfaces. The original structure and its complementary one exhibit naturally opposite chiral selectivity, which can be dynamically flipped by modulating the polarization angle of the incident light. The results reveal a competitive mechanism between the electromagnetic trapping potential and the chiral trapping potential. At a critical parameter, the two trapping potentials exactly cancel, leaving chiral nanoparticles completely free. Moreover, the maximum total trapping potential shifts from the fully chiral extrema (κ = ±1) to an intrinsically preferred optimal chirality parameter (κopt ≈ ±0.7). Our results advance the understanding of chiral optical trapping and provide a theoretical foundation for chiral sorting using a single geometry and its complement.